This sometimes can also be related to the internal batteries in the alarm ECU or alarm siren module going bad. If your handy the internal batteries can be replaced without buying a new replacement unit. Otherwise, the entire module must be replaced ($$$). Lastly, you can have a Saab indy or dealer disarm the theft alarm on the vehicle. You retain your keyless operation, but the alarm is not active. This is done in the programming and adjustment menus in the TWICE unit with the Saab Tech 2 computer.
Justin Duthie
Strictly Saab
Melbourne, FL

I've had similar problem, mine goes off a few minutes after locking due to faulty glass sensor, This can be disabled by following:
Switch off and remove key from ignition lock, then within 4 mins press and hold down Night switch (ie switch which turns most of display off when lights are on) until Door Alarm only appears. Then lock as usual